The present invention relates to smoking articles such as cigarettes, and in particular to catalytic systems containing metallic or carbonaceous particles that reduce the content of certain harmful or carcinogenic substances, including polyaromatic hydrocarbons, tobacco-specific nitrosamines, carbazole, phenol, and catechol, in both mainstream cigarette smoke and side stream cigarette smoke.
It is widely known that tobacco smoke contains mutagenic and carcinogenic compounds that cause substantial morbidity and mortality to smokers. Such compounds include polyaromatic hydrocarbons (PAHs), tobacco-specific nitrosamines (TSNAs), carbazole, phenol, and catechol.
The carcinogenic potential of polyaromatic hydrocarbons (PAHs) is well known. PAHs are a group of chemicals where constituent atoms of carbon and hydrogen are linked by chemical bonds in such a way as to form two or more rings, or xe2x80x9ccyclicxe2x80x9d arrangements. For this reason, these are sometimes called polycyclic hydrocarbons or polynuclear aromatics. Examples of such chemical arrangements are anthracene (3 rings), pyrene (4 rings), benzo(a)pyrene (5 rings), and similar polycyclic compounds.
Such compounds have been identified in all situations where combustion of organic materials is taking place, and where pyrolysis is incomplete. Several industrial sources of these compounds are known: incomplete pyrolysis of coke in metallurgy, in aluminum pot rooms, and of fuel oil in heat generating equipment, to name but a few. It is also known that internal combustion engines (diesel or gasoline engines) are a major source of these pollutants. Incomplete combustion of the most simple hydrocarbon, methane, often referred to as natural gas, has also been found to be a source of 3,4-benzopyrene emissions. PAHs have also been identified in tobacco smoke. Several of these PAHs are known to be carcinogens for lung tissue and others are suspected of similar effects, operating by genotoxic mechanisms, and their presence in tobacco smoke has further been linked with the synergism observed in smokers exposed to high levels of respirable dusts in uncontrolled workplace situations.
Tobacco specific nitrosamines (TSNAs) are electrophilic alkylating agents that are potent carcinogens. They are formed by reactions involving free nitrate during processing and storage of tobacco, and by combustion of tobacco containing nicotine and nornicotine in a nitrate rich environment. It is also known that fresh-cut, green tobacco contains virtually no tobacco specific nitrosamines. See, for example, U.S. Pat. Nos. 6,202,649 and 6,135,121 to Williams; and Wiernik et al., xe2x80x9cEffect of Air-Curing on the Chemical Composition of Tobacco,xe2x80x9d Recent Advances in Tobacco Science, Vol. 21, pp. 39 et seq., Symposium Proceedings 49th Meeting Tobacco Chemists"" Research Conference, Sep. 24-27, 1995, Lexington, Ky. In contrast, cured tobacco products obtained according to conventional methods are known to contain a number of nitrosamines, including the two most harmful carcinogens Nxe2x80x2-nitrosonornicotine (NNN) and 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK). Of these two, NNK is significantly more dangerous than NNN. It is widely accepted that such nitrosamines are formed post-harvest, during the conventional curing process, and in the combustion process.
Carbazole, phenol, and catechol are all compounds produced in cigarette smoke. Carbazole is a heterocyclic aromatic compound containing a dibenzopyrrole system and is a suspected carcinogen. The phenolic compounds in cigarette smoke are due to the pyrolysis of the polyphenols chlorogenic acid and rutin, two major components in flue-cured leaf. Currently, the literature identifies catechol, phenol, hydroquinone, resorcinol, o-cresol, m-cresol, and p-cresol as the seven phenolic compounds in tobacco smoke. Catechol is the most abundant phenol in tobacco smoke (80-400 xcexcg/cigarette) and has been identified as a co-carcinogen with benzo[a]pyrene (also found in tobacco smoke). Phenol has been shown to be toxic and is identified as a tumor promoter in the literature.
The most common method for removing harmful components from tobacco smoke is the use of a mechanical filter device. Various filters for reducing or removing undesirable components from tobacco have been proposed and constructed. In general, a porous filter may be provided as a mechanical trap for harmful components, interposed between the smoke stream and the mouth. This type of filter, often composed of cellulose acetate, mechanically or adsorptively traps a certain fraction of the components present in smoke.
Cigarette filter devices may contain a variety of granular or particulate adsorbents in addition to any porous materials, e.g., cellulose acetate tow, present in the device. Activated carbon, or charcoal, is the most widely preferred granular adsorbent. Other types of adsorbents include, for example, kaolin clay as disclosed in U.S. Pat. No. 4,729,389. U.S. Pat. No. 3,650,279 discloses a cigarette filter composed of a powdered aluminum silicate mineral that may be prepared by rendering the mineral electropositive and then cationizing it by absorbing macromolecular cations (such as methylene blue and FeSO4) thereon. U.S. Pat. No. 3,428,054 discloses a cigarette filter composed of mineral particles, such as slag, and absorptive powdered clay, such as kaolinite, bound together by a non-toxic binder. U.S. Pat. No. 3,251,365 discloses a cigarette filter composed of powdered clay, such as kaolin, into which from 1 to 13 percent by weight of iron or zinc oxide may be incorporated. U.S. Pat. No. 2,967,118 relates to a specially prepared kaolin clay powder which has been acid activated for use in filters. U.S. Pat. No. 4,022,223 teaches the use of alumina and activated alumina as base materials in absorptive filter compositions.
An improvement in the effectiveness afforded by mechanical-type filters or filters containing adsorptive materials may be provided by including means for chemically trapping or reacting undesirable components present in smoke. For example, U.S. Pat. No. 5,076,294 provides a filter element containing an organic acid, such as citric acid, which reduces the harshness of the smoke. Inclusion of L-ascorbic acid in a filter material to remove aldehydes is disclosed in U.S. Pat. No. 4,753,250. U.S. Pat. No. 5,060,672 also describes a filter for specifically removing aldehydes, such as formaldehyde, from tobacco smoke by providing a combination of an enediol compound, such as dihydroxyfumaric acid or L-ascorbic acid, together with a radical scavenger of aldehydes, such as oxidized glutathione or urea, or a compound of high nucleophilic activity, such as lysine, cysteine, 5,5-dimethyl-1,3-cyclohexanedione, or thioglycolic acid. U.S. Pat. No. 5,465,739, the contents of which is incorporated herein by reference in its entirety, discloses cigarettes incorporating a filter element containing an acidic material having a pKa at 25xc2x0 C. of less than about 3, such as phosphoric acid. U.S. Pat. No. 5,409,021 discloses a double or triple chamber cigarette filter containing lignin, which is effective in reducing levels of tobacco-specific nitrosamines.
While the filters present on most available cigarettes are effective in reducing levels of certain undesirable components in tobacco smoke, filters still allow a significant amount of undesirable compounds to pass into the mouth. Moreover, while filters may be preferred to reduce the amount of undesired components in mainstream smoke, which is the smoke that is drawn through the mouth end of a smokable article or device and inhaled by the smoker, filters do not reduce the amount of undesirable components in sidestream smoke. Sidestream smoke is the smoke that is given off from the end of a burning tobacco product between puffs and is not directly inhaled by the smoker. Sidestream smoke gives rise to passive inhalation on the part of bystanders, and is also referred to as second-hand smoke.
One approach to removing undesired components from tobacco smoke is the use of catalysts. Palladium catalyst systems have been proposed for cigarettes. The following patents describe such systems: U.S. Pat. No. 4,257,430 to Collins et al.; U.S. Pat. No. 4,248,251 to Bryant et al.; U.S. Pat. No. 4,235,251 to Bryant et al.; U.S. Pat. No. 4,216,784 to Norman et al.; U.S. Pat. No. 4,177,822 to Bryant et al.; and U.S. Pat. No. 4,055,191 to Norman et al., each of which is incorporated by reference in its entirety. Early attempts at incorporating catalytic systems into mass-produced cigarettes have met with limited success. Therefore, a catalytic system that reduces the levels of certain carcinogenic or otherwise undesirable components from tobacco smoke, and which is amenable to use in mass-produced cigarettes, is desirable.